Apparatus for freeing stuck pipe



Oct. 18, 1960 E. D. HALL 2,956,626

APPARATUS FOR FREEING STUCK PIPE Filed Aug. l, 1956 3 Sheets-Sheet 2 v i5 5' E l 2.9 4 i y ,d

A /lllmrllllllll/'fl/ll/ t INVENToR. .f5/mep /a// Oct. 18, 1960 E. D.HALL APPARATUS FOR FREEING sTucK PIPE 5 Sheets-Sheet 3 Filed Aug. 1,1956 TTOKNEK INVENTOR. E//We Ha# United States Patent.

APPARATUS FOR FREEING STUCK PIPE Elmer D. Hall, 401 Norton St.,Weatherford, Tex.

Filed Aug. 1, 1956, Ser. No. 601,579

13 Claims. (Cl. 166-177) This invention relates to methods and apparatusfor freeing stuck pipe in well bores and refers more particularly tosuch methods and apparatus wherein a rigid metallic length is forcedthrough the pipe to be unstuck, the metallic length having at least aportion thereof crooked or deformed and of suicient rigidity to deformthe pipe to be freed as it is forced therethrough.

Stuck pipe in this disclosure is to mean any type of pipe which has beenlowered into ak well bore for the purpose of drilling for, or productionof, water, oil, gas, etc., and has become lodged in the well bore insuch a manner that it cannot be lowered or withdrawn by present methodsof longitudinal tension (pulling on the pipe to its yield point) orcompression (applying the weight of the free pipe in the well boredownwardly upon the lodged or stuck pipe). Thus, the term stuck willdescribe pipe lodged in a well bore under the conditions describedabove.

One of the major concerns in finishing an oil Well -is sticking of thepipe and actually getting the pipe to the bottom of the hole. It wouldbe extremely desirable to be able to guarantee a job of getting the pipeto the bottom or keeping it free in the well bore if it is to be removedtherefrom. Previously, this has not been possible.

A number of conditions can actually happen in a well bore to stick pipetherein. enumerated as follows:

(-1) Where loose formations such as sand or shale have settled aroundthe pipe in the annulus between the outside of the pipe and the face ofthe well bore in a sucient quantity to cause enough friction that thepipe cannot be moved longitudinally or in rotation.

(2) Where a coupling or any other device that is on the pipe which is ofa larger diameter than the pipe becomes lodged in what is referred to inoil well drilling terminology as a key seat. A key seat is actually anenlargement in one side of the drilled Well bore caused by the movementof the pipe, either in rotation or in longitudinal movement, against theinside curve or bend opposite a bend or curve in the well bore. In sucha condition, the pipe is held against the inside curve or bend by thetension of pipe hanging below it, causing` the pipe to wear away thatside of the well bore to the same size of the pipe itself. In otherwords, a key seat is an attempt by the pipe in tension to straighten outor remove any deviations of the well bore from a straight line. Underthese conditions, any object of a larger diameter than the size of theWell bore at this key seat will tend to become wedged when forced intoit. In actual oil well drilling practice, the size of a key seat isdetermined by the tool joints or couplings on the drill pipe, and it isusually anydevice that has a larger diam.- eter than the tool jointsthat may become lodged therein.

(3) Where large objects in the hole, such as boulders, or broken or lostpieces of drilling tools become wedged between the pipe and the wellbore, causingv the pipe to stick.

These conditions can be ICC (4) Yet another condition in a well borewhich may stick pipe is differential pressure. In differential pressurehigh pressure liuid in the annulus between the casing and the well boreflows into a porous subterranean formation which has a natural pressurefar less than that of the annulus fluid. When this condition occurs, thecasing cleaves or seizes to the permeable portion of the borehole wallunder the inuence of the differential pressure. If the casing actuallycomes into contact with Athe porous or permeable formation, it acts as aseal over a greater or lesser area thereof and is thus forced againstthat region by an amount equal to the annulus pressure minus theformation pressure times the actual area of contact between the casingsexterior wall and the wall of the well bore. Thus, for example, if theannulus uid pressure exceeds the formation pressure by 1.800 pounds persquare inch, while the area of casing and borehole wall contact is 500square inches, the casing will be driven against the borehole Wall by atotal force of 400,000 pounds. It is obvious, that as long as theseconditions are maintained, there is little hope. of moving the casingfurther into the bore or removing it therefrom. The reason for this is,in the latter case,..that both the casing weight and the shear strengthof the contact plane must be overcome.

One of the great problems in oil well drilling is to salvage stuck pipe.Hundreds of millions yof dollars of pipe are left in wells every yearand only approximately 30% of the total pipe set in wells can besalvaged at present. Up to the present time, it has been possible onlyto salvage the casing down to the first oil sand in a multiple oilhorizon well because the first sand or any permeable, area thereabovecauses sticking ofthe pipe by differential pressure.

Therefore, an object of the invention is to provide method. andapparatus for freeing pipe which is stuck in a Well bore etciently anddependably.

Another object of the invention is to provide method and apparatus forfreeing pipe stuck in a well bore whether the pipe is stuck due tosettling of well material, key seat engagement, Wedging or differentialpressure.l

Another object of the invention is to provide apparatus for freeing pipestuck in a well bore wherein the apparatus may be either xed to thedrill stem andy lowered to the obstructed portion of the pipe thereon orforced there by hydraulic pressure.

Another object of the invention is to provide method and apparatus forfreeing pipe stuck in a well bore wherein pipe. stuck in a plurality oflpositions in a Well bore can be freed and, particularly, pipe stuckagainst a plurality of permeable sands by differential pressure can befreed.

Another object of the invention is to provide method and apparatus forfreeing pipe stuck in a well bore which will greatly increase thepercentage quantity of pipe which is salvageable from well bores, suchsalvage saving great quantities of both money and metal.

Another object of the invention is to provide method and apparatus forfreeing pipe `stuck in boreholes, the method and apparatus beingapplicable to free cemented pipe Where the bond is not complete or thecement has been contaminated, for example, it being common in oil wellcement jobs t-o have several hundred feet of contaminated cement at thetop of the cement portion. p Other and further objects ofthe inventionwill appear in the course of the following description thereof.

In the drawings, which form a part of the instant specification and areto be read in conjunction therewith, embodiments of the invention areshown and, in the various views, like numerals are used to indicate likeparts.

Fig. 1 is a cross-sectional view through an earth formation containing apermeable horizon therein, a-casingk Fig. 2 is a cross-sectional viewthrough an earth formal' tion having a permeable formation therein, acasing shown run in a well bore below the permeable horizon, a secondmodication of the inventive apparatus for freeing stuck pipe in the wellbore being shown positioned within the casing immediately above thestuck portion thereof.

Fig. 3 is a cross-sectional View through an earth formation showing apermeable formation therein, a casing having been run in awell borebelow the permeable formation and having become stuck thereto bydifferentiall pressure, a third modification of the inventive apparatusfor freeing stuck pipe shown positioned within the casing, the operativeportion of the apparatus being positioned opposite the permeable area.

Fig. 4 is a cross-sectional view through an earth formation having apermeable formation therein, a casing having been run in a well borebelow the permeable formation and a fourth modification of the inventionbeing shown positioned therein with the operative part` of the apparatuspositioned opposite the permeable area.`

Fig. 5 is a view taken along the line 5-5 of Fig. 4

Y in the directionof the arrows.

Fig. 6 is a cross-sectional view through an earth forma- -a permeableformation 11 therein.

It is assumed that the pressure of the permeable formation is less thanthat of the annulus so the annulus iiuid tends to flow thereinto. Casing13 is run in borehole 12 below the permeable formation 11 and, due tothe well bore condition of differential pressure, adheres to thepermeable formation as shown at 14. It is assumed that neither tensionnor pressure upon the casing is able to free it from the differentialpressure area. Therefore, the inventive apparatus for freeing pipe in awell bore is run into the casing to the vicinity of the stuck portionthereof. In this instance, the apparatus comprises a cylindrical, solidlength or crank of metal 15 which has an outer diameter slightly lessthan the inner diameter of the pipe to be freed, and a threaded upperend 16 to be engaged with the threaded lower end 17 of the drill stem18. The length 15 is crooked, bent or curved as at 15a over at least aportion thereof to a width greater than the internal diameter of thepipe to be unstuck and is of sufficient strength and rigidity to deformthe pipe to be freed as it is forced therethrough. Preferably, thelength is crooked, bent or curved centrally and has an essentiallyuniform slope on either side of the area of greatest bend up to thestraight end portions 15b and 15C. The width of the crooked or curvedportion of the length must be less than the smallest diameter of thewell bore to be passed through by the crank to reach the stuck tionhaving a permeable formation therein, a casing having been run in' awell bore below the permeable i formation, a fifth form of the inventiveapparatus for j unsticking pipe positioned within the casing, theoperative portion of the apparatus being positioned opposite thepermeable formation.

Fig. 7 is a cross-sectional view through an earth forma-1'" t tionhaving a permeable formation positioned therein, a casing having beenrun in a well bore below the permeable formationv and a sixth form ofthe inventive apparatus The invention comprises a preferably cylindricallength for unsticking pipe being shown positioned within the casing.

length crooked, bent or curved in at least a portion theref t of to aWidth greater than the internal diameter of thel pipe to be freed and ofsuicient strength or rigidity to deform 'the pipe to'be unstuck as it isforced therethrough. There are two basic modiiications of the invention.

rotary drill stem at the upper end thereof to be lowered at the end ofthe drill stem into the pipe to be freed to the stuck portion thereof.This modification of the invention is shown in Figs. l-5.

The flrstand preferred modification of the invention is such a lengthadapted to be attached to a y distor-t the stuck pipe to pass itselastic limit.

When the curved or...

crooked crank has been so lowered to the vicinity' of thejammed portionof the pipe to be freed, it may be rotated at thelower end of the drillstem to free the pipe from the obstructed area.

The second modification of the invention, which isA u shown in Figs. 6and 7, comprises such a described length of metal having means atthe topthereof to permit the j length to be forced down the pipe to be freed byhydraulic pressure. This form may not be rotated in the vicinity ,of orat the stuck portion of the casing and, thus, must rely merely upon theeffect of the motion of its form i "i through the obstructed portion ofthe pipeto free it. Certain structural changes may be employed in bothof the two basic modifications and will be set forth in detail in thefollowing:

Referring iirst to Fig. l, therein is shown a firsty mod iiication .ofthe drill `stern suspended apparatus .for `unsticking pipe. At 10 isshown an earth formation having applied at the wellhead.

portion of the pipe. If surface casing or pipe has been set, the widthof the crooked portion of the length must be less than the internaldiameter of the surface pipe as well as the internal diameter of thehole bore. The

`length of the crank or length 15 is not critical but is the weight ofthe drill stem pipe becomes sufficient to force it through the casingwithout extra force being It is evident that the entire casing traversedby the crank 15 will be deformed as it passes therethrough in the mannershown in Fig. l; that is, the casing takes the shape of the crank as thelatter passes through it. It is desirable that the width of the crookand the length thereof be such that the casing does not pass its elasticlimit in its deformation, but, in some extreme circumstances, it may benecessary to employ a crank or eccentric length of a form that will In apreferred variation of the method, the crank or length 15 is forceddownwardly through the casing 13 until the f crooked or curved portion15a of the length approaches the stuck portion of the pipe. Before thecrooked portion 15a of the crank` reaches the stuck portion of the pipe,rotation of the crank is begun by rotating the drill stem 18. Then,gradually, the crank 1S is moved downwardly, continuing rotation, untilthe crooked portion 15a is opposite the cleavage area. In this way, thedestruction of the cleavage plane of the casing 13 to the formation 11will be progressive rather than entire and simultaneous. The crank maybe moved entirely below the stuck portion in rotation if desired. Whenthe casing 13 is wedged, blocked or in a key seat, it is easy to seethat such rotation will serve to break up and displace the Wedgingmaterial to free the pipe. In a differential pressure sticking, thepassage of the well bore iluids into the permeable zone packs anddehydrates the mud in the .well bore against the permeable zone and,once the casthe formation pore space and serve to sealoff the permeableformation even more and, thereforethe tendency will be for the casingnot to restick. i

When there are several permeable formations or stuck portions of thecasing, the crank or length should be forced first above the rst stuckzone, then rotated and moved into the stuck zone to free it. Once thatzone has been cleared, the crank is then forced downwardly to a positionabove the second zone, rotation begun and then the crank moved into thezone while rotating. In this manner, the pipe may be freed from anindefinite number of stuck zones and the running of the casing to thebottom of the hole or its removal. from the hole may be guaranteed. Oncethe stuck areas have: been freed, the drill stern and crank arewithdrawnfrom the casing. Contaminated or faulty cement jobs will sometimes leavecasing or pipe in such a condition of adherence to the well bore thatthe inventive crank may be ableto beat several hundred feet of thecasing free from the faulty bond to permit the recovering thereof. Insome situations, however, and this is a variation of the method, it maybe desirable to actually move the crank downwardly into the obstructedportion of the. pipe before rotation thereof is begun.

In Fig. 2 is shown a modification of the drill stem attached form of thecrank or length wherein the actual length is a hollow tube threaded atthe upper end thereof to attach to the drill stem. In Fig. 2, 19indicates the earth formation, 20 a permeable formation therein, 21shale or other debris which has wedged the casing 22 adjacent thepermeable formation and 23 the well bore which has been drilled belowthe formation. Tubing 24 has hollow annulus 25, crooked, bent or curvedportion 24a and an open lower end with threaded portion 26 at the upperend thereof to engage the threaded portion 27 of drill stem 28. Thecrank 24, although hollow, must be of sufficient strength to deform thecasing 22 to its shape as in the modification of Fig. l. While in theFig. l modification, the crank or length 15 was formed to an outerdiameter only slightly less than the inner diameter of the casing so asto deform the casing 13 essentially uniformly without putting too greata stress on limited areas of the casing, Fig. 2 shows a modification ofthe invention wherein bearings are employed at the contact pointsbetween the crank and the casing to minimize wear on the tool or crank24. In such a case, the crank itself is generally of proportionatelyless outer diameter relative the inner diameter of the casing Whereby tohave bearings 29 of sufficient lthickness to stand long term wear. Thebearings 29 are of an outer diameter less than the inner diameter of thecasing 22 whereby to permit forcing of the crank down through the casingwith the only deformation of the casing being due to the crooking orbending of the crank itself. The bearings 29 are preferably positionedat the area of greatest bend of the crank and at the ends of the bentportion thereof, which areas normaly will carry the friction ofinsertion, forcing through the pipe and rotation therein. Additionalbearings may be required between the central bearing and the endbearings if the crank is of unusual length.

The operation of the Fig. 2 modification is the same as that of the Fig.l modification with the bearing mounted, hollow tube crank 24 beingthreaded onto the drill stern, forced down the casing 22 to the vicinityof the stuck portion of the pipe and rotation thereof within the casingbegun either before or after the bent por-tion of the crank is forcedinto the stuck portion of the casing. It should be noted, that the Fig.1 modification, that is, a solid bar crank or length, could be employedwith bearings of the same type as Fig. 2 merely by employing a solid barof slightly lesser diameter and fixing the bearings thereto.Additionally, the Fig. 2 modification,V a hollow tube, could be employedwithout bearings the differences noted, the construction, form, strengthand operation of the Fig. 2 modification is the same as that of the Fig.1 modification.

Figs. 3 and 4 illustrate a modification of the invention wherein thecrank is attached to the drill stem for rotation at its upper end and isformed so as to permit lubrication of the outside of the crank or toolduring insertion, motion through or rotation in the pipe to reducefriction and wear. Fig. 3 shows the lubricating modification employingbearings as described relative the Fig. 2 modiiication` and Fig. 4 showsthe lubrication modification without the use of bearings. Referringfirst to Fig. 3, earth formation 30 has permeable formation 31 therein.Well; bore 32 extends below the permeable formation 31 and earthformation 30 and casing 33 is run therein below the permeable formationand has become stuck thereto byl differential pressure. Fig. 3 alsoshows the modification of the, method wherein the crank is runcompletely into. the obstructed area before rotation thereof is begun.In the lubrication modification, the crank 34 comprises a hollow tubebent, curved or crooked as at 34a, having an annulus 35 sealed as at 36at its lower end. Perforations. 37 cut through the wall of the tubing34. Threaded portion 38 of the crank 34 engages threaded portion 39 ofdrill stem 40., While the crank 34 is being forced through the casing 33into the obstructed area, lubricating liquid or material may be forcedout through the perforations 37 from the annulus 35 of the crank and thedrill stem. This lubricating material may be used to reduce frictioneither in forcing thetool down the casing or in the rotation of the toolonce it is positioned relative the stuck area of the pipe. When bearings41 are employed at the contact points of the crank, as shown in Fig. 3,the tubing 34 is of slightly lesser outer diameter relative the innerdiameter of the casing than a bearingless crank and the bearings 41 areof an outer diameter only slightly less than the inner diameter of thecasing. Preferably, when bearings 41 are employed, perforations 37 areformed on each side of the bearings so that the bearings will not blockow of the lubricating material over the entire outer surface of thecrank and all the bearings.

Referring to Fig. 4, the lubricating modification is shown without thebearings. Earth formation 42 has permeable formation 43 therein. Wellbore 44 is drilled through the permeable formation and casing 45 is runbelow said formation. Hollow tubing 46 having an outer diameter onlyslightly less than the inner diameter of the casing and having crookedportion 46a is run into the stuck portion of the casing against thepermeable formation 43. The drawing has cut off the lower portion o-fthe crank but it is intended that the lower end thereof be sealed as inFig. 3. Perforations 47 communicate with annulus 48 of the tubing.Threaded portion 49 of the upper end of the tubing is fastened tothreaded portion 50 of drill stem 51. The lubricating material, as inthe Fig. 3 modification, may be forced out of the perforations as thecrank 46 is moved through the casing to be freed or when it ispositioned ready for rotation therein. Fig. 5 shows the effect ofrotation of the crank 46 in the casing as the crank is rotated. Sincethe Width of the bent portion of the crank is less than the diameter ofthe borehole of the well, the casing 45 (full and dotted lines) does notabrade or wear excessively against the well wall when the crank isrotated. Aside from the differences noted, the limitations andcharacteristics of the cranks in Figs. 3 and 4 are the same as those inFigs. 1 and 2 (depending on whether or not bearings are employed) as tostrength, size, length, shape, operation, etc. Both the Fig. 3 and Fig.4 modifications are shown run into the jammed length of the casingbefore rotation, but both may be set into rotation before freeing thepipe is begun. l

A variation of the operation in the drill stem attached modification(Figs. 1 4), lies in running the crank into V'the stuck portion of thepipe and then merely rotating the crank therein 180, whereby to tlex thepipe away from the wall once only. This variation materially reduces atthe end of the drill stem.

Figs. 6 and 7 show the secondary modification of the i invention whereinthe crank or length of metal is not iixed -wear on crank, drill stem andcasing. Conventional well .practice easily measures and controls thecrank rotation to the end of the drill stem to be lowered orforced orlength of metal 57 has curved, deformed or crooked portion 57a and is ofa strength or rigidity whereby to cause the pipe 55 through which itpasses to deform to assume the shape of the tool. The diameter of thesolid metal bar 57 is preferably only slightly less than that of thepipe through which it passes. The width of the deformed portion 57a isless than that of the surface casing, if any, and the well bore throughwhich it passes. The top end S8 of the tool is of lesser diameter topermit the mounting of packers 59 and 60 thereon. Packer mountingthimbles 6I Iare fixed to the lesser diameter portion 58 of the tool andsupport the packers 59 and 60 against hydraulic pressure exerted thereonfrom above.

In operation of this modification of the invention, `the packers aremerely mounted on the crank or tool 57, the tool inserted into thecasing, and hydraulic pressure exerted therebehind to force the crankdownwardly through the casing. The hydraulically driven crank reliesentirely upon the deformation of the tool and the resultant deformationof the pipe as it passes therethrough to dislodge the pipe from itsengagement with the wall. While the drill stem mounted cranks may beemployed in this manner, rotation thereof is more effective. In Fig. 6,the lower end of the crank 57 is already passed through the jammedportion of the pipe and thus the pipe is shown -as partly freed from thedifferential pressure sealing. When the tool has been forced through theobstruction, it may be forced through any other lower obstructed area ofthe pipe to free it as desired. It is not possible to remove the toolfrom the pipe in this modification without removing the pipe from thehole, `and this is the preferred method of recovering it. However, ifdesired, the tool may be merely forced down below any production areaand left in the pipe or blown out of the end of the pipe which is thenrecovered free of the tool. The Fig. 6 modification of the inventionworks well in all stuck pipe situations with the exception of certainkey seat blocks. It is possible for a tool as shown in Fig. 6 to beforced through a certain type of key seat block without freeing the pipefrom the Well wall. The modification of the packer mountinghydraulically driven form shown in Fig. 7 does not suffer from thisdefect. It should be noted that the tool in the Fig. 6 showing need notbe solid all the way through but it should be sealed either at the upperor lower end to prevent flow of the hydraulic fluid therethrough.

Fig. 7 shows a spiral modification of the tool of Fig. 6. Earthformation 62 has permeable formation 63 therein. Well bore 64 extendsthrough the permeable formation yand therebelow. Casing 65 has been runthrough and rbelow the permeable formation and is jammed thereat bydifferential pressure as at 66. To unstick lcasing 65 from its adhesionto permeable formation 63, rigid, casing deforming, spiral crank 66having lesser diameter portion the casing by hydraulic pressure. Thewidth of the spirals in the length or crank 66 is greater than thediameter of the casing 65 so that the casing is deformed as at 70a,

v71, 72 and y73 as the crank is forced therethrough. NoYfInaYttei-.A.what the cause of the jamming or sticking of the pipe,Vthe forcing of the crank 66 through the obstruction will causedeformation of the pipe and exert the desired force thereon to free itfrom the cause of the sticking. -Other'than' the difference in shape,and a somewhat lesser farfeais the saine also.

It `should be understood that while the cylindrical form is preferred onall of the cranks or elements shown in ethe drawings and described inthe specification, any desired form, triangular, square, hexagonal,etc., in cross section may be employed so long as the greatest diameterofthecross-sectional form is not greater than the ,inside diameter ofthe pipe to be freed. The usefulness of the ,cylindrical form lies inits minimizing of friction and localized Wear on the pipe as it passestherethrough and is rotated therein.

From the foregoing it will be seen that this invention is one welladapted to attain all of the ends and objects hereinabove lset forthtogether with other advantages which are obvious and which are inherentto the structure and method.

It will be understood that certain features and subcombinations are ofutility and may be employed without reference to other features andsubcombinations. This is contemplated by and is within the scope o-f theclaims.

As many possible embodiments may be made of the invention withoutdeparting from the scope thereof, it is to be understood that all matterherein set forth is to be interpreted as illustrative and not in alimiting sense.

Having thus described my invention, I claim:

1. Apparatus for flexing pipe positioned in a well bore comprising anelongate body of metal, said body having a greatest outer diameter lessthan the inner diameter of the pipe to be :flexed and a lengthsubstantially greater than the inner diameter of the said pipe, saidbody crooked within its length whereby to form a rigid working toolhaving an effective diameter between its extremities greater than theinner diameter of the pipe to be flexed, said body of substantiallygreater strength `and rigidity than the pipe to be exed, said bodystrength and rigidity sufficiently greater than that of the pipe to betiexed whereby to flex the said pipe when the body is positioned thereinand further ex the pipe when said body is moved or rotated therein.

2. Apparatus as in claim l wherein said body is cylindrical.

3. Apparatus as in claim l wherein said body has a circumferentialfriction bearing in the area of greatest displacement from the axis ofthe body.

4; Apparatus as in claim l wherein said body has circumferentialfriction bearings adjacent the ends of the crooked portion therein.

5. Apparatus as in claim l wherein said body has a circumferentialfriction bearing in the area of greatest displacement from the axis ofthe body and circumferential friction bearings adjacent the ends of thecrooked portion thereof.

6. Apparatus as in claim 1 wherein said body is crooked centrallythereof and has essentially uniform curvature on either side of thecentral portion thereof.

7. Apparatus as in claim 1 including means to attach said body to adrill stem on one end thereof.

8. Apparatus as in claim l wherein said body has packing means at oneend thereof whereby to permit the length to be forced through the pipeto be liexed hydraulically.

9. Apparatus as in claim 1 wherein said body is formed of a solid pieceof metal.

9 10 10. Apparatus as in claim 1 wherein said body has 13. Apparatus asin claim 1 wherein the crooked pormeans to attach it to a drill stem onone end thereof and tion of the length is formed in spiral conguration.

comprises a hollow tube open at both ends thereof.

11. Apparatus as in claim 1 wherein said body is a Refr c Ctd' thlofth'st t hollow tube with one end sealed and the other end wlth 5 e en es l em e e l pa en means to attach it to a drill stem and at least one UNITEDSTATES PATENTS opening in the side wall communicating with the an-52,102 Witsil Jan. 16, 1866 nulus thereof intermediate the ends thereof.1,699,087 Woodmansee et al Jan. l5, 1929 12. Apparatus as in claim 1wherein the effective ydiam- 2,011,036 Colmerauer Aug. 13, 1935 eter ofthe crooked portion of the body is less than the 10 2,336,334 ZublinDec. 7, 1943 smallest diameter of the well bore to be passed through2,340,959 Harth Feb. 8, 1944 by the body. 2,730,176 Herbold Jan. 10,1956

